I am a prime number.
The double of myself is equal to the square of me.

which number am I?

Find the number of squares in the below picture

There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?

During which month do people sleep the least?

Can it be possible to build a house that has all its four walls facing towards the South?

Take away my first letter, then take away my second letter. Then take away the rest of my letters, yet I remain the same. What am I?

Can you circle exactly four of these numbers such that the total is twelve?

1 6 1
6 1 6
1 6 1
6 1 6

You walk into a room that contains a match, a kerosene lamp, a candle and a fireplace. What would you light first?

When 99 is considered higher than 100?

2, 3, 5, 9, 17, _ What is the next number in the sequence?